Water Filtration Ratios: What They Do and What to Look For

Water is roughly 98% of brewed coffee, and it is the ingredient most people never examine. Composition changes extraction as much as grind does.

What is actually happening

Minerals in water bind to flavour compounds in coffee and carry them into solution. Magnesium is particularly effective at extracting the compounds associated with sweetness and fruit; calcium contributes body but also forms scale.

Bicarbonate is the other half of the story. It buffers acidity — it neutralises the bright, fruity acids you may have paid for. High-bicarbonate water makes even a lively coffee taste flat and dull.

So there is a genuine target range, not simply "purer is better".

The numbers worth knowing

The Specialty Coffee Association's water standard is a useful reference:

What goes wrong at either extreme

Too soft — under roughly 75 mg/L, and distilled or reverse-osmosis water especially — extracts inefficiently. There is little for flavour compounds to bind to. The cup reads thin and hollow no matter how you adjust dose or grind. This is why pure RO water makes disappointing coffee.

Too hard — over 250 mg/L — mutes aromatics, and the high alkalinity that usually accompanies it flattens acidity. It also builds scale in every heated component you own.

Chlorinated tap water is the easiest fix on this page. Chlorine is volatile and detectable at very low concentrations, and a simple carbon filter removes it.

Practical options, in order of effort

1. Carbon filter jug. Removes chlorine and some hardness. Cheapest meaningful improvement available.
2. Bottled water with a published mineral analysis. Read the label and look for something in the ranges above. Many popular mineral waters are far too hard.
3. RO or distilled water plus a mineral concentrate. Full control, consistent, and the route most competition brewers take.

Espresso machines specifically

Scale is the main killer of heated equipment. If you own a machine with a boiler, softened or properly filtered water is not about flavour alone — it is what determines whether the machine lasts five years or fifteen.